import collections
class Solution(object):
    def uncommonFromSentences(self, s1, s2):
        """
        :type s1: str
        :type s2: str
        :rtype: List[str]
        """
        out = []
        s1 = s1.split(' ')
        s2 = s2.split(' ')
        c1 = collections.Counter(s1)
        c2 = collections.Counter(s2)
        for key in c1:
            if c1[key] == 1 and not c2[key]:
                out.append(key)
        for key in c2:
            if c2[key] == 1 and not c1[key]:
                out.append(key)
        return out


data = Solution()
s1 = "this apple is sweet"
s2 = "this apple is sour"
print(data.uncommonFromSentences(s1, s2))